The invention relates to a tube coupling which is produced by shrink fitting a first tube part onto a second tube part.
It is known from GB Patent 903,757 that a synthetic resin tube made of thermoplastic material is fastened to a fixed hose connection by first being expanded and then shrunk onto the hose connection. The hose connection has annular ridges in the form of locking ribs on its circumference.
It is also known from German OS 28 24 205 to fasten an air intake tube to the cylinder head of an internal combustion engine in which a prefabricated annular bead is provided at the end of the air intake tube. This bead is gripped by means of a flange ring with an internally positioned elastomer ring and then the flange ring is fastened to a flange surface of the cylinder head. In this known kind of attachment, a plurality of components must thus be held simultaneously, and by means of relatively complicated clamping and threading procedures they must be attached at places on the cylinder head which as a rule are not easily accessible.
It is the object of the invention to provide a tube coupling and a method for its production by simple steps and appropriate materials which can be handled with few and simple means and which assures a lastingly secure connection even under special circumstances of use.
The generic tube coupling with a first tube part of thermoplastic synthetic resin material and a tube connector as a second tube part onto which the tube can be shrunk is further developed in accordance with the invention in that the first tube part is a blow-molded synthetic resin part, and the second tube part is an injection molded synthetic resin part, wherein both tube parts have approximately equal coefficients of thermal expansion throughout a wide temperature range with respect to longitudinal and transverse expansion.
In a preferred application, the first tube part is advantageously a component of an air intake tube in the air intake tract of an internal combustion engine and the other tube part is a flange part on the cylinder head of the internal combustion engine for fastening the first tube part. Both tube parts must here withstand starting or operating temperatures in a range from xe2x88x9240xc2x0 C. to +150xc2x0 C. and should nevertheless lastingly assure a tight fit without additional fastening materials.
In order in this case to achieve a lessening or equalization of the thermal expansion coefficients in an advantageous manner, the first tube part is, according to the invention, a blow-molded synthetic resin part made of polyamide with a longitudinal thermal expansion coefficient of approximately 0.2xc2x710xe2x88x924/K and a transverse thermal expansion coefficient of about 1.0xc2x710xe2x88x924/K, and the second tube part is an injection-molded synthetic resin part made of polyamide with a longitudinal thermal expansion coefficient of approximately 0.35xc2x710xe2x88x924/K and a transverse thermal expansion coefficient of approximately 1.2xc2x710xe2x88x924/K.
With the material properties stated above, the stretch elongation in the stated temperature range can advantageously be limited to about 12% and the expansion of the tube parts to about 8% (corresponding to about 3 mm for a nominal width of 40 mm). The maximum difference between the overlapping tube parts here amounts to only about 0.1 mm in the stated temperature range, which assures a durable, tight fit between the joined tube parts.
Suitable materials for the tube parts include, advantageously, for the first tube part PA66Gf35 and for the second tube part PA6Gf10 or PA6Gf15. In a manner known in itself, annular locking ribs, which act opposite to the direction of the first tube part, can be provided on the second tube part in the seating area where the first tube part is shrunk onto it.
In a method for joining the tube parts, the first tube part can be expanded in the cold state in the area where it will overlap the second tube part and the first tube part can be slipped with its expanded portion over the second tube part. By heating this area a shrinkage and subsequent tight fitting of the first tube part onto the second tube part is produced. According to the invention, the inside diameter prior to expansion is smaller than the outside diameter of the second tube part, and after expansion it is slightly larger than the outside diameter of the second tube part.
In a simple production step the first tube partxe2x80x94here preferably an air intake tube to be attached to the cylinder headxe2x80x94is expanded in the cold state in the area where it will overlap the second tube part, here preferably the flanged piece for fastening to the cylinder head. In this area of the first tube a mechanical tension is thus frozen into the circumference, whereby the inside diameter prior to expansion was smaller than the outside diameter of the other tube part and after expansion is slightly larger than the outside diameter of the other tube part.
In the second production step the expanded region of first tube part is slipped in an advantageous manner onto the other tube part and by heating this region it is made to shrink and fit tightly on the second tube part. Thus, the heating releases the circumferential tension frozen in during the cold expansion again and results in a tight constriction around the other tube part.
With this method according to the invention it is thus possible in a simple manner for the second tube part, for example, the separate flange part, to be attached to the first tube part prior to the final installation of the first tube, and then both parts together can be fastened by simple means to the cylinder head of an internal combustion engine.
These and additional features of preferred embodiments of the invention will be found not only in the claims but also in the description and the drawings, the individual features being applicable individually or jointly in the form of subcombinations in embodiments of the invention and in other fields and may represent advantageous as well as independently patentable embodiments, for which protection is hereby claimed.